Crosstalk between NGS Receptors, TrkA & P75

描述(申请人提供)：神经营养因子在神经系统正常发育和维持所需的细胞过程中发挥关键的调节作用，如细胞生存/死亡、轴突生长/引导和突触传递/可塑性。Trk受体和p75都参与介导这些不同的神经营养因子作用，但p75主要负责成人发育特定阶段或病理条件下神经营养因子依赖的细胞死亡。这个项目的总体目标是了解NGF在细胞死亡和生存方面行动的信号机制，重点是受p75调控的Rac和Rho。P75以一种与细胞凋亡相关的方式长期激活RAC，而Trk/p75的共同激活导致RAC的短暂激活和细胞存活。这些结果表明，RAC激活的动力学可能是细胞存活和死亡之间的关键决定因素。另一方面，对Rho的调节可能取决于p75与哪个辅助受体相关联：与神经营养因子/Trk一起，p75抑制Rho，而它激活Rho作为Nogo受体NGR的辅助受体。P75通常是由成人神经系统损伤引起的，在这种情况下，它的表达与细胞凋亡有关。在导致p75和细胞死亡的实验性损伤后，Rho被激活，这表明通过p75控制Rho的激活将是防止细胞死亡和损伤后退化的关键。因此，我们的总体假设是，p75对Rac和Rho的调控决定了细胞死亡和存活/再生之间的结果。为了了解p75激活RAC和Rho的机制，我们发现Kalirin家族的胍交换因子，Kalirin7和9与p75结合。Kalirin7含有一个Rac全环基金结构域，而Kalirin9同时含有RAC和RHO全环基金结构域。其具体目的包括：(1)确定Kalirin7对Rac短暂激活的机制，(2)确定延长Rac激活是否对细胞凋亡是必要的，(3)确定Kalirin9是否在体外和体内调节相反的p75对脊髓损伤后Rho活性的作用。这项研究的结果将通过阐明p75和Trk以及p75和NGR之间复杂相互作用背后的基本生化机制，大大提高对NGF信号转导的现有知识。对这些机制的详细了解可能最终会促使在神经元损伤和疾病的情况下促进再生和限制变性的治疗策略。

DESCRIPTION (provided by applicant): Neurotrophins play key regulatory roles in cellular processes that are required for proper development and maintenance of the nervous system, such as cell survival/death, axon growth/guidance, and synaptic transmission/plasticity. Both Trk receptors and p75 participate in mediating these diverse neurotrophin actions, but p75 is mainly responsible for neurotrophin-dependent cell death at specific stages during development or under pathological conditions in the adult. The overall goal of this project is to understand the signaling mechanisms that underlie NGF's action regarding cell death and survival, with a focus on Rac and Rho, which are regulated by p75. P75 activates Rac in a prolonged manner that correlates with apoptosis, while co-activation of Trk/p75 leads to transient Rac activation and cell survival. These results suggest that the kinetics of Rac activation may be the key determinant in cellular outcome between cell survival and death. Regulation of Rho, on the other hand, may be determined by which coreceptor that p75 associates with: With neurotrophins/Trk, p75 inhibits Rho, while it activates Rho as a co-receptor for the Nogo receptor, NgR. P75 is often induced by injury in the adult nervous system and its expression in such cases has been linked to apoptosis. After the experimental injuries that induced p75 and cell death, Rho was activated, suggesting that controlling Rho activation by p75 will be critical in preventing cell death and degeneration after injuries. Our overall hypothesis is therefore that regulation of Rac and Rho by p75 determines the outcome between cell death and survival/regeneration. In an effort to understand the mechanisms by which p75 activates Rac and Rho, we discovered that the Kalirin family of guanidine exchange factors (GEF), Kalirin7 and 9, bind p75. Kalirin7 contains a Rac GEF domain, while Kalirin9 contains both Rac and Rho GEF domains. The specific aims include: (1) To determine the mechanisms of transient Rac activation by Kalirin7, (2) To determine whether prolonged Rac activation is necessary for apoptosis, and (3) To determine whether Kalirin9 is responsible for regulating the opposite's action of p75 for Rho activity both in vitro and in vivo after spinal cord injury. The outcome of this study will result in significant advancement of the current knowledge of NGF signaling, by elucidating the basic biochemical mechanisms behind the complex interplay between p75 and Trk, as well as p75 and NgR. A detailed understanding of the mechanisms may ultimately prompt therapeutic strategies for promoting regeneration and limiting degeneration in cases of neuronal injury and disease.