Nerve Growth Factor (NGF) promotes the elaboration of axonal filopodia and branches through PI3K-Akt. NGF activates the TrkA receptor resulting in an initial transient high amplitude burst of PI3K-Akt signaling followed by a maintained lower steady state, hereafter referred to as initiation and steady state phases. Akt initially undergoes phosphorylation at T308 followed by phosphorylation at S473, resulting in maximal kinase activation. We report that during the initiation phase the localization of PI3K signaling, reported by visualizing sites of PIP3 formation, and Akt signaling, reflected by Akt phosphorylation at T308, correlates with the positioning of axonal mitochondria. Mitochondrial oxidative phosphorylation but not glycolysis is required for Akt phosphorylation at T308. In contrast, the phosphorylation of Akt at S473 is not spatially associated with mitochondria and is dependent on both oxidative phosphorylation and glycolysis. Under NGF steady state conditions, maintenance of phosphorylation at T308 shows dual dependence on oxidative phosphorylation and glycolysis. Phosphorylation at S473 is more dependent on glycolysis but also requires oxidative phosphorylation for maintenance over longer time periods. The data indicate that NGF induced PI3K-Akt signaling along axons is preferentially initiated at sites containing mitochondria, in a manner dependent on oxidative phosphorylation. Steady state signaling is discussed in the context of combined contributions by mitochondria and the possibility of glycolysis occurring in association with endocytosed signalosomes.

神经生长因子 (NGF) 通过 PI3K-Akt 促进轴突丝状伪足和分支的形成。NGF 激活 TrkA 受体，导致 PI3K-Akt 信号传导的初始瞬时高振幅爆发，随后保持较低的稳态，以下称为起始和稳态阶段。Akt 最初在 T308 处发生磷酸化，然后在 S473 处发生磷酸化，从而最大限度地激活激酶。我们报告说，在起始阶段，PI3K 信号的定位（通过可视化 PIP3 形成的位点）和 Akt 信号（通过 T308 处的 Akt 磷酸化反映）与轴突线粒体的定位相关。Akt 在 T308 的磷酸化需要线粒体氧化磷酸化而不是糖酵解。相比之下，Akt 在 S473 的磷酸化在空间上与线粒体无关，并且依赖于氧化磷酸化和糖酵解。在 NGF 稳态条件下，T308 磷酸化的维持表现出对氧化磷酸化和糖酵解的双重依赖性。S473 的磷酸化更依赖于糖酵解，但也需要氧化磷酸化以维持较长时间。数据表明，NGF 诱导的沿轴突的 PI3K-Akt 信号传导优先在含有线粒体的位点以依赖于氧化磷酸化的方式启动。在线粒体的综合贡献和与内吞信号体相关的糖酵解的可能性的背景下讨论了稳态信号。