Tat mediation of HIV-associated mood disorders via functional deficits in brain

描述（由申请人提供）：抑郁和焦虑是“神经艾滋病”综合征的常见情绪障碍症状，对hiv阳性患者的治疗和健康构成重大问题。不幸的是，将hiv相关神经病理学与神经回路功能障碍和行为情绪障碍的进展联系起来的生物学机制尚不清楚。最近的证据表明，像Tat这样的hiv附属蛋白可能从hiv感染的细胞扩散到整个大脑，产生神经毒性和神经元活动的变化，这可能是导致行为变化的原因。我们假设Tat蛋白的表达足以导致神经退行性变和调节情绪的神经回路功能障碍，从而导致抑郁和焦虑样行为的增加。本研究利用GT-tg转基因小鼠及其强力霉素基因诱导策略，在大脑中控制、选择性地表达Tat蛋白。诱导的GT-tg基因小鼠将被用于通过行为和成像研究来验证这一假设，即tat介导的抑郁和焦虑样行为的增加与tat诱导的与抑郁和焦虑相关的大脑结构和功能的改变有关，包括杏仁核、前扣带、眶额皮质和海马。这些小鼠的行为研究将通过强迫游泳压力和社会厌恶测试来评估Tat表达如何影响抑郁样行为。行为学实验还将采用开阔场地、高架加迷宫、明暗箱、声惊吓和埋弹珠实验来研究Tat表达对焦虑类行为的影响。Tat mRNA和蛋白水平的测定将把Tat的表达与观察到的行为变化联系起来。在初步研究中，tat诱导的小鼠比未诱导的同伴在社会交往中花费的时间更少，在强迫游泳压力测试中花费的时间更多，这表明tat介导的抑郁样行为增加。tat诱导的小鼠也表现出焦虑相关行为的增加，在露天环境中花费的时间更少，大理石埋葬的时间增加了3倍。同时，我们将利用超高磁场强度的离体磁共振成像（MRI）和TUNEL染色检测Tat诱导的动物细胞凋亡，研究Tat蛋白对脑结构和细胞死亡的影响。初步的离体结构成像研究表明，在表达tat的小鼠中，杏仁核和海马的灰质密度显著降低。此外，我们将使用皮质酮激发的BOLD功能MRI来识别与情绪障碍相关的大脑区域的功能变化，这些变化是由不同水平的诱导和暴露于Tat蛋白的持续时间以及对皮质酮激发剂量的反应引起的。总的来说，该项目旨在证明在Tat诱导的动物的脑回路中可以检测到功能和结构缺陷，从而确定Tat可能介导神经艾滋病特征情绪障碍的机制。

DESCRIPTION (provided by applicant): Depression and anxiety are prevalent mood disorders symptomatic of the syndrome described as "NeuroAIDS," and pose significant problems for the treatment and well-being of HIV-positive patients. Unfortunately, the biological mechanisms linking HIV-related neuropathology to the dysfunction of neuronal circuitry and the progression of behavioral mood disorders are not well understood. Recent evidence suggests that HIV-accessory proteins such as Tat may spread throughout the brain from HIV-infected cells, producing neurotoxicity and changes in neuronal activity that could account for the behavioral changes. We hypothesize that Tat protein expression is sufficient to produce neurodegeneration and dysfunction of neuronal circuitry mediating mood, resulting in an increase of depression- and anxiety-like behaviors. This proposal utilizes the GT-tg transgenic mouse and its doxycycline-gene induction strategy for a controlled, selective expression of Tat protein in the brain. Induced GT-tg bigenic mice will be used to test the hypothesis with behavioral and imaging studies that Tat-mediated increases in depression- and anxiety-like behaviors are correlated with Tat-induced alterations in brain structure and function in regions associated with depression and anxiety, including the amygdala, anterior cingulate, orbitofrontal cortex and hippocampus. Behavioral studies with these mice will assess how Tat expression affects depression-like behaviors with the forced swim stress and social aversion tests. Behavioral experiments also will examine effects of Tat expression on anxiety-like behaviors using the open field, elevated plus maze, light-dark box, acoustic startle and marble burying tests. Assays of Tat mRNA and protein levels will correlate expression of Tat to the observed changes in behavior. In preliminary studies, Tat-induced mice spent less time than uninduced littermates in social interactions and more time immobile in forced swim stress tests, suggestive of a Tat-mediated increase in depression-like behavior. Tat-induced mice also demonstrated increased anxiety-related behaviors, with less time spent in open-field environments and a 3-fold increase in marble burying. Concurrently, we will examine the effects of Tat protein on brain structure and cell death using ex vivo magnetic resonance imaging (MRI) at ultra high magnetic field strength and TUNEL staining for apoptosis in Tat-induced animals. Preliminary ex vivo structural imaging studies documented significant reductions in the grey matter density of amygdala and hippocampus in Tat-expressing mice. Additionally, we will use BOLD functional MRI with corticosterone challenge to identify functional changes in brain regions associated with mood disorders resulting from varying levels of induction and duration of exposure to Tat protein and the response to a challenge dose of corticosterone. Overall, this project seeks to prove that functional and structural deficits can be detected in the brain circuitry of Tat-induced animals, thereby defining mechanisms by which Tat may mediate the mood disorders characteristic of NeuroAIDS.