Dopamine Signaling Mechanisms of Traumatic Brain Injury

描述（由申请人提供）：认知缺陷，特别是记忆障碍，是创伤性脑损伤后最常见的持续性残疾，由纹状体、边缘系统和额叶皮层的破坏引起。我们小组和其他人的实验和临床证据暗示多巴胺（DA）系统的改变是造成这种缺陷的原因。此外，在实验模型和I期人体研究中，da增强剂可以减轻功能缺陷。然而，对于da介导的缺陷的细胞信号机制以及da增强剂在脑外伤后赋予其有益作用的机制知之甚少。纹状体是一个重要的DA信号的位置。长期以来，人们一直认为纹状体是运动功能的调节器，最近发现它通过与边缘系统和皮层的联系，对学习和记忆功能至关重要。纹状体中DA信号的干扰尚未在任何创伤性脑损伤的实验模型中得到研究。DA-和环腺苷单磷酸（cAMP）调节的磷酸化蛋白Mr 32 kDA （DARPP-32）是纹状体中棘神经元中多种神经递质系统（包括DA）活性的关键汇聚点。DARPP-32的趋同特性与两个不同的磷酸化位点苏氨酸34 （Thr34）和苏氨酸75 （Thr75）有关，这两个磷酸化位点拮抗调节细胞内信号分子。特别是，DARPP-32 Thr34位点的磷酸化是camp -胞外调节激酶（ERK1/2）通路的重要介质，作为蛋白磷酸酶1 （PP1）的抑制剂。该项目代表了DARPP-32信号通路作为tbi诱导的功能缺陷机制的首次研究。我们的研究将验证脑外伤导致纹状皮质神经元DARPP-32磷酸化功能障碍的假设，这可能导致ERK1/2级联反应的改变和工作记忆缺陷。我们将测量脑外伤对这个重要的细胞内信号汇合点的影响。在修订后的项目中，我们将首先研究TBI对DARRP-32和关键下游效应物的影响。其次，我们打算确定在Thr34磷酸化位点增加DARPP-32的磷酸化是否可以减弱tbi诱导的相同关键下游信号变化和功能缺陷的变化。第三，我们将评估DARPP-32在介导临床相关的康复期间经常给予的DA增强剂的积极作用。最后，为了更好地确定DARPP-32变化、治疗和后续结果变量之间的因果关系，我们提出了利用DARPP-32敲除（KO）模型的补充实验。这些研究结果将阐明脑外伤后纹状体-皮层功能，并为支持针对与DA激动剂治疗脑外伤相关的下游生化途径的临床研究提供初步的临床前证据。公共卫生相关性：在美国，创伤性脑损伤（TBI）占所有伤害相关死亡的三分之一以上。在幸存者中，创伤性脑损伤会导致认知功能的持续障碍。该项目旨在研究认知缺陷的关键神经化学机制，并评估新的治疗方法，以最大限度地恢复功能。

DESCRIPTION (provided by applicant): Cognitive deficits, particularly memory impairments, are the most common persistent disability after TBI, resulting from disruptions in the striatum, limbic system, and frontal cortex. Experimental and clinical evidence from our group and others implicates altered dopamine (DA) systems in contributing such deficits. Furthermore, in experimental models and in Phase I human studies, DA-enhancing agents can attenuate functional deficits. However, little is known about the cellular signaling mechanisms underlying DA-mediated deficits and the mechanisms by which DA-enhancing agents confer their beneficial effects after TBI. The striatum is a location of significant DA signaling. Long considered a modulator of motor function, the striatum more recently was found to be vital to learning and memory function through connections with the limbic system and cortex. Disturbances in DA signaling in the striatum have not been investigated in any experimental model of TBI. The DA- and cyclic adenosine monophosphate (cAMP)-regulated phosphoprotein, Mr 32 kDA (DARPP-32), is a key convergence point in striatal medium spiny neurons for the activity of multiple neurotransmitter systems, including DA. The convergent properties of DARPP-32 are related to the two distinct phosphorylation sites, threonine 34 (Thr34) and threonine 75 (Thr75), which act antagonistically to regulate intracellular signaling molecules. In particular, DARPP-32 phosphorylation at Thr34 is an important mediator of the cAMP-extracellular regulated kinase (ERK1/2) pathway, acting as an inhibitor of protein phosphatase 1 (PP1). This project represents the first examination of the DARPP-32 signaling pathway as a mechanism for TBI-induced functional deficits. Our study will test the hypothesis that TBI causes dysfunction of DARPP-32 phosphorylation in striato-cortical neurons, which may contribute to alterations in ERK1/2 cascades and working-memory deficits. We will measure the effects of TBI on this important intracellular signaling convergence point. In the revised project, we will first examine the effects of TBI on DARRP-32 and key downstream effectors. Second, we propose to determine if increasing phosphorylation of DARPP-32 at the Thr34 phosphorylation site can attenuate TBI-induced changes in the same key downstream signaling changes, and functional deficits. Third, we will evaluate the role of DARPP-32 in mediating the positive effects of a clinically relevant DA enhancer that is frequently given during rehabilitation. Lastly, to better determine causal relationships between DARPP-32 changes, treatments, and subsequent outcome variables, we propose complementary experiments that utilize a DARPP-32 knockout (KO) model. The results of these studies will clarify striato-cortical function after TBI and provide initial preclinical evidence to support clinical studies targeting downstream biochemical pathways associated with DA agonist therapies for TBI. PUBLIC HEALTH RELEVANCE: In the United States traumatic brain injury (TBI) accounts for over one third of all injury related deaths. In survivors, TBI results in the persistent disturbance of cognitive functioning. This project seeks to examine key neurochemical mechanisms underlying cognitive deficits and to evaluate novel therapies to maximize recovery of function.