ION CHANNEL MODULATION BY THE PRION PROTEIN: A NOVEL TOXIC MECHANISM

描述（由申请人提供）：现在对朊病毒的化学性质和它们的传播机制有了很大的了解。相比之下，异常形式的朊蛋白（PrP）如何杀死神经细胞仍然是一个谜。有证据表明，朊病毒的神经毒性在于它们能够改变或破坏PrPC （PrP的细胞形式）的正常生理功能，但这一过程的细节尚不清楚。Tg (?表达残基105-125缺失突变PrP的CR)小鼠，为朊病毒相关致病机制提供了强有力的见解。这些动物自发地发展为严重的神经退行性疾病，通过野生型PrP的共表达以剂量依赖性的方式逆转。我们一直有兴趣阐明PrP的强大毒性背后的细胞和分子机制。CR：我们最近发现？CR缺失作为一种显性的功能获得突变，强烈激活PrP固有的或由PrP间接诱导的离子通道活性。此外，我们发现PrP中心区域的疾病相关点突变具有类似的作用，这表明一些家族性朊病毒疾病是由于离子通道的兴奋毒性激活引起的。在这个应用中，我们建议对朊病毒疾病的“离子通道假说”进行严格的测试。首先，我们将调查PrP中心区域所有已知的人类突变对体外离子通道活性的影响。然后，我们将对在中心区域携带点和缺失突变的PrP分子诱导的通道的生物物理特性进行表征。最后，我们将确定嗜离子性谷氨酸受体的兴奋毒性激活是否在突变PrP分子和感染性PrPSc诱导的神经元死亡和神经病理中起作用。该项目阐明的致病机制可能具有广泛的适用性，因为离子通道的异常激活在许多其他神经退行性疾病和动物模型中都是一个很好的范例。此外，鉴定prp介导毒性的特定离子通道靶点将是开发一种全新的抗朊病毒药物的第一步，这种药物可以抑制细胞神经毒性途径，而不是PrPSc的传播。

DESCRIPTION (provided by applicant): A great deal is now known about the chemical nature of prions and the mechanism by which they propagate. In contrast, how abnormal forms of the prion protein (PrP) kill nerve cells is still a mystery. There is evidence that the neurotoxicity of prions lies in their ability to alter or subvert a normal, physiological function of PrPC, the cellular form of PrP, but the details of this process are obscure. Tg(?CR) mice, which express a mutant PrP deleted for residues 105-125, provide powerful insights into prion related pathogenic mechanisms. These animals spontaneously develop a severe neurodegenerative illness that is reversed in a dose-dependent fashion by co-expression of wild-type PrP. We have been interested in elucidating the cellular and molecular mechanisms underlying the powerful toxicity of PrP?CR. We have recently discovered that the ?CR deletion acts as a dominant, gain-of-function mutation that strongly activates an ion channel activity that is intrinsic to, or is indirectly induced by, PrP. Moreover, we have found that disease-associated point mutations in the central region of PrP have a similar effect, suggesting that some familial prion diseases are due to excitotoxic activation of ion channels. In this application, we propose to critically test an "ion channel hypothesis" of prion diseases. First, we will survey all known human mutations in the central region of PrP for their effect on ion channel activity in vitro. We will then undertake characterization of the biophysical properties of the channels induced by PrP molecules carrying point and deletion mutations in the central region. Finally, we will determine if excitotoxic activation of ionotropic glutamate receptors plays a role in the neuronal death and neuropathology induced by mutant PrP molecules and infectious PrPSc. The pathogenic mechanisms elucidated in this project are likely to have wide applicability, since abnormal activation of ion channels is a well established paradigm in a number of other neurodegenerative diseases and animal models. Moreover, identification of specific ion channel targets for PrP-mediated toxicity would represent the first step in development of an entirely new class of anti-prion drugs that inhibit cellular neurotoxic pathways, rather than PrPSc propagation. PUBLIC HEALTH RELEVANCE: Prion diseases are fatal neurodegenerative disorders of humans and animals that pose a grave threat to public health, and endanger the safety of the food, blood and organ supplies. This application will explore a novel mechanism of prion pathogenesis based on abnormalities in the ion channels that control electrical activity in the nervous system. This project represents the first step in development of an entirely new class of anti-prion drugs that inhibit cellular neurotoxic pathways, rather than prion propagation.