Department of Neuroscience and Physiology, State University of New York Upstate Medical University, Syracuse, NY 13210.
Developmental Exposure to Alcohol Research Center (DEARC), Binghamton University, Binghamton, NY 13902.
eNeuro. 2020 Jul 28;7(4). doi: 10.1523/ENEURO.0168-20.2020. Print 2020 Jul/Aug.
Disruptions in neuronal dendrite development alter brain circuitry and are associated with debilitating neurological disorders. Nascent apical dendrites of cortical excitatory neurons project into the marginal zone (MZ), a cell-sparse layer characterized by intense chondroitin sulfate proteoglycan (CSPG) expression. Paradoxically, CSPGs are known to broadly inhibit neurite growth and regeneration. This raises the possibility that the growing apical dendrite is somehow insensitive to CSPG-mediated neurite growth inhibition. To test this, developing cortical neurons were challenged with both soluble CSPGs and CSPG-positive stripe substrates Soluble CSPGs inhibited dendritic growth and cortical dendrites respected CSPG stripe boundaries, effects that could be counteracted by prior CSPG inactivation by chondroitinase. Importantly, addition of Reelin, an extracellular signaling protein highly expressed in the MZ, partially rescued dendritic growth in the presence of CSPGs. High-resolution confocal imaging revealed that the CSPG-enriched areas of the MZ spatially correspond with the areas of reduced dendritic density in the Reelin null () cortex compared with controls. Chondroitinase injections into explants resulted in increased dendritic growth into the MZ, recovering to near wild-type levels. Activation of the serine threonine kinase Akt is required for Reelin-dependent dendritic growth and we find that CSPGs induce Akt dephosphorylation, an effect that can be counteracted by Reelin addition. In contrast, CSPG application had no effect on the cytoplasmic adaptor Dab1, which is rapidly phosphorylated in response to Reelin and is upstream of Akt. These findings suggest CSPGs do inhibit cortical dendritic growth, but this effect can be counteracted by Reelin signaling.
神经元树突发育的中断会改变大脑回路，并与使人衰弱的神经紊乱有关。皮质兴奋性神经元的初始顶树突投射到边缘区（MZ），MZ 是一个细胞稀疏的层，特征是强烈表达软骨素硫酸盐蛋白聚糖（CSPG）。矛盾的是，CSPG 已知广泛抑制神经突生长和再生。这就提出了这样一种可能性，即生长中的顶树突对 CSPG 介导的神经突生长抑制具有某种不敏感性。为了检验这一点，研究人员用可溶性 CSPG 和 CSPG 阳性条纹底物来挑战发育中的皮质神经元。可溶性 CSPG 抑制树突生长，皮质树突尊重 CSPG 条纹边界，这些效应可以通过软骨素酶预先灭活 CSPG 来逆转。重要的是，在存在 CSPG 的情况下，添加在 MZ 中高度表达的细胞外信号蛋白 Reelin 部分挽救了树突生长。高分辨率共聚焦成像显示，MZ 中富含 CSPG 的区域与 Reelin 缺失（）皮层中树突密度降低的区域在空间上相对应，与对照相比。软骨素酶注入 外植体导致树突向 MZ 生长增加，恢复到接近野生型水平。丝氨酸苏氨酸激酶 Akt 的激活是 Reelin 依赖性树突生长所必需的，我们发现 CSPG 诱导 Akt 去磷酸化，而 Reelin 的添加可以逆转这种效应。相比之下，CSPG 处理对细胞质衔接蛋白 Dab1 没有影响，Dab1 对 Reelin 反应迅速发生磷酸化，并且位于 Akt 的上游。这些发现表明 CSPG 确实抑制皮质树突生长，但这种效应可以被 Reelin 信号逆转。
