Survival and growth-promotion mechanisms of the GDNF family ligands (GFLs)

描述（由申请人提供）：胶质细胞系源性神经营养因子（GDNF）家族配体（GFL）是调节神经系统发育和成人神经系统维持的四种同源神经元生长因子。GFLs促进存活并增强在神经退行性疾病如帕金森病中受影响的几个神经元群体的代谢和表型状态，即营养状态。GFLs的这些有效的存活和营养活性已经导致其作为治疗剂用于治疗神经系统的疾病和损伤的发展。为此，对GFLs在生理条件下的作用机制的理解将有助于设计利用GFLs的治疗方案。在发育过程中，GDNF具有远距离功能，如促进轴突生长和运动神经元的靶依赖性存活。然而，GDNF或其他GFLs是否能够在仅激活位于其轴突末端的受体时支持神经元的存活和生长尚不清楚。此外，神经元生长因子维持神经元营养状态的机制还没有很好地建立。神经生长因子（NGF）是生长因子的神经营养蛋白家族的成员，其通过激活GFLs的异源受体酪氨酸激酶Ret来调节交感神经元的营养状态。值得注意的是，NGF并不通过产生GFL来激活Ret，而是通过TrkA、NGF受体和Ret之间的串扰机制来起作用。我的实验室拥有罕见的能力，可以使用区室化培养物对原代神经元的分离轴突和细胞体进行生化和细胞生物学实验，使这些重要问题落入我们的掌握之中。作为我们描绘神经营养因子在发育和成人神经系统中的作用机制的长期目标的一部分，我们提出以下建议：1）检验GDNF作为长距离存活和生长促进因子的假设，2）检验GDNF受体Ret在活化时的下调决定GDNF的局部和长距离信号传导能力的假设，3）验证NGF通过调节受体酪氨酸激酶的两个重要调节因子Cbl-3和CD 2AP抑制Ret的活性依赖性降解而增强Ret活化的假设。GDNF家族配体（GFL）目前正在研究用于治疗神经变性疾病如帕金森病、亨廷顿病、ALS和视网膜疾病，以及用于治疗神经系统损伤如脊髓损伤（SCI）和中风。Neurturin是这个家族的一员，目前正在进行帕金森病的II期临床试验。因此，理解GFLs的局部和远距离信号传导能力以及理解GFLs传递存活和生长的分子机制将有助于设计采用GFLs的治疗策略。

DESCRIPTION (provided by applicant): The glial cell line-derived neurotrophic factor (GDNF) family ligands (GFLs) are four homologous neuronal growth factors that regulate the development of the nervous system and the maintenance of the adult nervous system. GFLs promote the survival and enhance the metabolic and phenotypic status, i.e. trophic status, of several populations of neurons that are affected in neurodegenerative diseases such as Parkinson's disease. These potent survival and trophic activities of the GFLs has led to their development as therapeutic agents for the treatment of diseases and injuries of the nervous system. To this end, an understanding of the mechanisms of action of the GFLs under physiologic conditions will aid in the design of treatment regimens that utilize the GFLs. During development, GDNF has long-distance functions, such as the promotion of axon growth and target-dependent survival of motor neurons. However, whether GDNF, or other GFLs, are capable of supporting the survival and growth of neurons when only activating receptors located on their axon terminals is unclear. Furthermore, the mechanisms by which neuronal growth factors maintain the trophic status of neurons are not well established. Nerve growth factor (NGF), a member of the neurotrophin family of growth factors, regulates the trophic status of sympathetic neurons via activation of Ret, the heterologous receptor tyrosine kinase for the GFLs. Remarkably, NGF does not activate Ret through the production of GFLs, and instead NGF acts via a cross-talk mechanism between TrkA, the NGF receptor, and Ret. My laboratory has the rare ability to conduct biochemical and cell biological experiments on isolated axons and cell bodies of primary neurons using compartmentalized cultures, bringing these important questions within our grasp. As part of our long-term goal of delineating the mechanisms of action of neurotrophic factors in the developing and adult nervous system we propose the following: 1) to test the hypothesis that GDNF acts as a long-distance survival and growth-promoting factor, 2) to test the hypothesis that the down regulation of the GDNF receptor, Ret, upon activation dictates the local and long-distance signaling capabilities of GDNF, 3) to test the hypothesis that NGF augments Ret activation via the inhibition of the activity-dependent degradation of Ret through the modulation of Cbl-3 and CD2AP, two important regulators of receptor tyrosine kinases. The GDNF family ligands (GFLs) are currently being investigated for the treatment of neurodegenerative diseases such as Parkinson's disease, Huntington's disease, ALS, and retinal diseases, and for injuries of the nervous system such as spinal cord injury (SCI) and stroke. Neurturin, a member of this family, is currently in phase II clinical trials for Parkinson's disease. Therefore, an understanding of the local and long-distance signaling capacities of the GFLs and an understanding of the molecular mechanisms by which GFLs convey survival and growth will aid in the design of treatment strategies that employ GFLs.