Interplay between neuroprotective pathways, HIV, and astrocytes

 描述(由申请人提供)：星形胶质细胞-神经元通信轴的崩溃正在成为一些神经退行性疾病的共同特征，包括艾滋病毒相关的神经认知障碍(HAND)。即使在联合抗逆转录病毒治疗的时代，HAND也会影响大约50%的艾滋病毒感染者，而且随着艾滋病毒感染者年龄的增长，其流行率预计会增加。这突显了需要更好地定义驱动艾滋病毒介导的神经发病的细胞和分子机制，以设计新的策略来预防和/或治疗手部疾病。我们确定Wnt/β-连环蛋白通路是星形胶质细胞中艾滋病毒高效复制的限制因素。Wnt/β-连环蛋白对细胞的调节作用 结构、突触活性、细胞增殖和存活率。该途径的中心介体(β-连环蛋白)与转录因子结合，并与同源基因连接以调节其活性。我们发现β-catenin通过在+1位与HIV LTR143位与Tcf-4和SMAR-1形成复合体，抑制POL II对接，从而抑制HIV转录，从而限制HIV。这些研究首次确定了HIV启动子上的功能性TCF-4结合位点，并确定了它们在500个HIV分离株中的流行率。有趣的是，炎性介质如干扰素γ或HIV-1Tat抑制β-连接素活性，而β-连接素信号抑制神经炎性转录因子CAAT/增强子结合蛋白(C/EBP)。我们现在提供的证据表明，星形胶质细胞中Wnt/β-Catenin的破坏对神经元产生负面影响。具体地说，我们发现在体外和体内抑制β-Catenin信号转导对星形胶质细胞清除谷氨酸的能力有显著的影响，这是通过抑制兴奋性氨基酸转运蛋白2(啮齿类动物的EAAT-2/GLT-1)和谷氨酰胺合成酶(GS)的表达来实现的。谷氨酸过量是神经艾滋病和其他神经退行性疾病的共同特征。此外，我们还发现，较高的血浆Dickkopf相关蛋白1(Dkk1，Wnt信号的可溶性拮抗剂)水平与HIV感染者的整体神经认知功能较差有关，这表明Dkk1可能是手的生物标记物。这些集体研究提供了我们的中心假设，即星形胶质细胞内β-连环蛋白信号的减弱将扰乱星形胶质细胞的关键功能，限制其神经保护特性。为了验证这一假说，我们将确定星形胶质细胞中Wnt/β-catenin信号减弱对体外和体内神经元损伤的功能后果(目标1)，通过抑制C/EBP导致促炎细胞因子/趋化因子、星形胶质细胞激活和白细胞浸润减少来评估Wnt/β-catenin信号激活物通过抑制C/EBP减少和/或改善艾滋病毒相关神经炎症过程的能力(目标2)，并使用来自CNS HIV抗逆转录病毒治疗效果研究(Charge)和加州神经艾滋病组织网络(CNTN)研究的精心设计的样本来确定与Wnt/β-catenin信号相关的分子是否是临床和神经病理生物标志物。总之，这些研究将促进我们对神经保护途径(Wnt/β-Catenin)和星形胶质细胞/神经元轴之间相互作用的理解，这样做将对神经退行性疾病具有更广泛的适用性，为翻译研究提供一条途径。

 DESCRIPTION (provided by applicant): A breakdown in astrocyte-neuronal axis of communication is emerging as a common feature in a number of neurodegenerative diseases, including HIV-Associated Neurocognitive Disorder (HAND). Even in the combined antiretroviral therapy era, HAND affects approximately 50% of HIV infected individuals and its prevalence is expected to increase as the HIV-infected population ages. This underscores the need to better define cellular and molecular mechanisms driving HIV-mediated neuropathogenesis to devise novel strategies to prevent and/or treat HAND. We determined that the Wnt/β-catenin pathway is a restriction factor for productive HIV replication in astrocytes. Wnt/β-catenin regulates cell structure, synaptic activity, cell proliferation, and survival. The central mediator of this pathwa (β-catenin) binds to TCF/LEF transcription factors and tethers on cognate genes to regulate their activity. We showed that β-catenin restricts HIV by forming a complex with TCF-4 and SMAR-1 on the HIV LTR at site -143 from the +1 site to inhibit Pol II docking and consequently inhibits HIV transcription. These studies led to the first identification of functional TCF-4 bindig sites on the HIV promoter and established their prevalence in 500 HIV isolates. Interestingly, inflammatory mediators such as IFNγ or HIV-1 Tat suppress β-catenin activity while β-catenin signaling inhibits the neuroinflammatory transcription factor CAAT/enhancer-binding proteins (C/EBP). We now provide evidence to suggest that disruption of Wnt/β-catenin in astrocytes negatively impact neurons. Specifically, we show that suppression of β-catenin signaling in vitro and in vivo has a dramatic effect on the ability of astrocytes to scavenge for glutamate by inhibiting the expression of Excitatory Amino Acid Transporter 2 (EAAT-2/GLT-1 in rodents) and glutamine synthetase (GS). Excess glutamate is a common feature in neuroAIDS and other neurodegenerative diseases. Further, we show that higher plasma levels of Dickkopf-related protein 1 (DKK1, a soluble antagonist of Wnt signaling) are associated with worse global neurocognitive functioning among people living with HIV, suggesting that DKK1 may be a biomarker of HAND. These collective studies inform our central hypothesis which states that diminished β-catenin signaling within astrocytes in response to an inflammatory mediator and/or HIV will perturb key functions of astrocytes and limit their neuroprotective properties. To test ths hypothesis, we will determine the functional consequences of diminished Wnt/β-catenin signaling in astrocytes on neuronal injury in vitro and in vivo (Aim 1), assess the ability of activators of Wnt/β-catenin signaling to reduce and/or ameliorate HIV associated neuroinflammatory processes by inhibiting C/EBP leading to reduction in proinflammatory cytokines/chemokines, astrocyte activation and leukocyte infiltration (Aim 2), and determine whether molecules related to Wnt/β-catenin signaling are clinical and neuropathological biomarkers of HAND using well-defied samples from the CNS HIV Anti-Retroviral Therapy Effects Research (CHARTER) and California NeuroAIDS Tissue Network (CNTN) studies. Together, these studies will advance our understanding of the interplay between a neuroprotective pathway (Wnt/β-catenin) and the astrocyte/neuronal axis of communication and in doing so will have a broader applicability to neurodegenerative diseases to provide a path for translational studies.