The role of protein phosphatase 2A in age-related memory impairment

描述（由申请人提供）：不同程度的记忆丧失发生在衰老过程中，即使在其他方面健康的人。对抗与年龄相关的记忆丧失（ARML）的尝试将受益于有关大脑机制的知识。许多蛋白质的功能根据磷酸基团被激酶添加或被磷酸酶去除的程度而变化。这些酶活性的不平衡会破坏细胞内信号通路，而这些信号通路是调节基因表达和细胞功能变化所必需的，而这些变化是学习和记忆发生所必需的。蛋白磷酸酶（PP） 2A是作用于细胞外受体激酶（ERK）类丝裂原活化蛋白激酶（MAPK）的主要酶。5型代谢性谷氨酸神经递质受体（mGluR5）沿神经元质膜与活性PP2A形成复合物。当谷氨酸与mGluR5受体结合时，该复合物解离，使PP2A失活，并允许活化的磷酸化形式的ERK （pERKs）积累。这些刺激核磷酸化蛋白的水平，如Elk-1，形成dna结合复合物，激活几种基因的表达。这种信号传导级联的中断会损害学习和记忆。在衰老过程中，功能性mGluR5受体数量和pERK活性的减少表明，ARML可能代表了一种整合神经元突触传递失败，无法产生记忆相关基因表达所需的细胞内pERK阈值水平。为了绕过丢失的受体并提高pERK水平，我们建议使用基因传递技术过表达I1PP2A，一种天然的PP2A蛋白抑制剂。基于腺相关病毒（AAV）的载体将用于26个月大鼠的双侧海马注射，这些大鼠表现出与年龄相关的学习和记忆能力障碍。在I1PP2A或对照基因转移后4周，重新评估海马依赖性和独立型迷宫任务的习得和保留。基因转移和行为重新评估后收获的海马组织将用于转基因表达的组织学评估。我们假设I1PP2A治疗将使年龄损伤正常化。此外，我们预测学习和记忆的改善将与PP2A活性降低、pERK水平升高以及下游靶点pElk-1、pCREB、c-fos、zif/268和arc的上调相对应。公共健康相关性：随着年龄的增长，许多人的记忆功能会下降。这个计划中的项目将测试大脑中一种生化信号系统的破坏是如何解释老年老鼠学习或记忆能力下降的。这一结果可能为治疗与年龄相关的记忆功能障碍提供新的药理靶点。

DESCRIPTION (provided by applicant): Variable degrees of memory loss occur during aging, even in otherwise healthy people. Attempts to counteract age-related memory loss (ARML) will benefit from knowledge of the brain mechanisms involved. Many proteins vary in function according to the extent to which phosphate groups are added by kinases or removed by phosphatases. Imbalance in these enzymatic activities can disrupt intracellular signaling pathways necessary to mediate changes in gene expression and cellular function that are required for learning and memory to occur. Protein phosphatase (PP) 2A is the primary enzyme acting on the extracellular receptor kinase (ERK) class of mitogen-activated protein kinases (MAPK). The type 5 metabotropic glutamate neurotransmitter receptor (mGluR5) forms a complex with active PP2A along the neuronal plasma membrane. This complex dissociates when glutamate binds to mGluR5 receptors, inactivating PP2A and allowing the accumulation of the activated, phosphorylated forms of ERK (pERKs). These stimulate levels of nuclear phosphoproteins, such as Elk-1, to form DNA-binding complexes that activate the expression of several genes. Interruption of this signal transduction cascade impairs learning and memory. Reduction in the number of functional mGluR5 receptors, and pERK activity, during aging suggest that ARML may represent a failure of integrated neuronal synaptic transmission to generate a threshold level of intracellular pERK necessary for the expression of memory-related genes. To bypass the lost receptors and boost pERK levels, we propose using a gene delivery technique to overexpress I1PP2A, a natural protein inhibitor of PP2A. A vector based on adeno-associated virus (AAV) will be used for bilateral hippocampal injections in 26-month rats exhibiting an age-related impairment in learning and memory performance. Acquisition and retention of hippocampal-dependent and independent maze tasks will be re-evaluated 4 weeks after I1PP2A or control gene transfer. Hippocampal tissue harvested after gene transfer and behavioral reassessment will be used for histological evaluation of transgene expression. We hypothesize that treatment with I1PP2A will normalize age-impairment. Further, we predict that the improvement in learning and memory will correspond with decreased PP2A activity, increased levels of pERK, and upregulation of downstream targets pElk-1, pCREB, c-fos, zif/268 and arc. PUBLIC HEALTH RELEVANCE: Many people experience a decrease in memory function as they age. The proposed project will test how disruption of one biochemical signaling system in the brain might account for a reduced ability for aged rats to learn or remember. The results could lead to new pharmacological targets for treating age-related memory dysfunction.