Neuronal paxillin and drebrin mediate BDNF-induced force transduction and growth cone turning in a soft tissue-like environment

Soft tissue environments govern neuronal morphogenesis. However, the precise molecular mechanisms underlying chemotropism-directed axonal growth cone movement in extremely soft environments remain unclear. Here, we show that drebrin, a growth cone T-zone protein, modulates growth cone turning in response to BDNF coated on a soft substrate. Structurally, axonal growth cones of rodent hippocampal neurons grown on 0.1 kPa hydrogels possess an expanded T-zone in which drebrin is highly integrated with both F-actin and microtubules. Biochemically, we identify paxillin as interacting with drebrin in cells grown on 0.1 kPa hydrogels but not on glass coverslips. When grown on 0.1 kPa substrates, growth cones asymmetrically exposed to BDNF-bound stripes exhibit enhanced paxillin/drebrin interaction on the side facing the stripes, an activity that is PKA- and AAK1-dependent, but independent of Src kinase. Functionally, we show that BDNF-induced growth cone turning and force generation on soft substrates require drebrin phosphorylation and paxillin/drebrin association.

软组织环境调控神经元的形态发生。然而，在极端柔软环境中，化学趋导性轴突生长锥运动背后的精确分子机制尚不明确。本研究中，我们发现drebrin，一种生长锥T区蛋白，能够调节生长锥在BDNF（脑源性神经营养因子）涂层软基质上的转向。在结构上，培养在0.1 kPa水凝胶上的啮齿动物海马神经元轴突生长锥具有一个扩大的T区，其中drebrin与F-肌动蛋白和微管高度整合。在生化层面上，我们发现在0.1 kPa水凝胶上生长的细胞中paxillin与drebrin相互作用，而在玻片上生长的细胞中则无此现象。当生长在0.1 kPa基质上时，不对称暴露于BDNF结合条纹的生长锥在面向条纹的一侧表现出增强的paxillin/drebrin相互作用，这一活动依赖于PKA和AAK1，但与Src激酶无关。在功能上，我们发现BDNF诱导的软基质上生长锥的转向和力生成需要drebrin的磷酸化和paxillin/drebrin的结合。