Evaluation of antidepressant-like effects of hippocampal HCN channel modulation

描述(由申请人提供)：难治性抑郁症出现在超过一半的严重抑郁障碍(MDD)患者中，并与高残疾和自杀率有关。大多数现有的MDD治疗方法都是针对大脑通路，涉及单胺类神经递质5-羟色胺、去甲肾上腺素和多巴胺。由于治疗耐药率高，专注于非单胺类机制的新疗法可能会带来重大突破，拯救许多人的生命。抑郁症患者大脑的一个区域是海马体，它也是抗抑郁药物作用的重要靶点。在海马体内，一种称为超极化激活环核苷酸门控(HCN)通道的离子通道帮助控制神经元的兴奋性。HCN通道调节一种电流(Ih)，该电流对处理神经元之间的突触信号至关重要。HCN通道沿着神经元树突的长度表达水平越来越高，这种亚细胞定位对于HCN通道在信号处理中的作用是重要的。HCN通道的定位受其辅助亚单位TRIP8b(含四肽重复序列的Rab8b相互作用蛋白)的严格调控。我们的实验室最近发现，HCN通道亚单位的基因缺失会导致小鼠出现抗抑郁药样表型。此外，其他人发现，使用抑制性RNA减少海马区的HCN1也能产生类似的抗抑郁作用，这表明HCN通道功能可能是治疗抑郁症的靶点。HCN通道对大脑和心脏的许多功能至关重要，因此抑制HCN通道的药物方法可能会产生有害的副作用。相比之下，使用病毒载体的解剖学靶向基因治疗提供了精确控制基因表达时间和地点的好处。在初步研究中，我们发现，使用腺相关病毒(AAV)感染海马区，在筛选抗抑郁活性的测试中，使用腺相关病毒(AAV)来阻止海马神经元中HCN亚单位的正常运输(但不是表达绿色荧光蛋白的对照AAV)显著减少抑郁样行为。因此，我们推测病毒载体介导的抑制背侧海马区HCN通道的基因治疗是治疗抑郁症的有效方法。为了验证这一假说，我们将使用免疫组织化学、生化、电生理学和行为学研究来完成以下特定目标：1)确定针对HCN通道的病毒基因治疗是否可以在小鼠身上产生特异和持久的抗抑郁药样作用；以及2)确定针对HCN通道的病毒基因治疗是否可以有效消除遗传和环境抑郁症模型中的抑郁样行为。总体而言，我们提议的工作将评估一种新的靶点和创新的抑郁症治疗策略，有别于所有当前的治疗方法，最终目标是将这种治疗方法转化为未来对患有抑郁症的患者的研究。 现有治疗方法无法治愈的抑郁症。

DESCRIPTION (provided by applicant): Depression refractory to medical treatment is seen in over half of patients with Major Depressive Disorder (MDD) and is associated with high rates of disability and suicide. Most existing treatments for MDD target brain pathways involving the monoaminergic neurotransmitters serotonin, norepinephrine and dopamine. Because of high rates of treatment resistance, new therapies focusing on non-monoaminergic mechanisms could lead to major breakthroughs, saving many lives. One region of the brain altered in patients with depression is the hippocampus, which is also an important target for the action of antidepressants. Within the hippocampus, an ion channel called the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel helps control neuronal excitability. HCN channels mediate a current (Ih) that is critical for processing synaptic signals between neurons. The HCN channel is expressed at increasingly higher levels along the length of neuronal dendrites, and this subcellular localization is important for the HCN channel's role in signal processing. HCN channel localization is tightly regulated by its auxiliary subunit, TRIP8b (tetratricopeptide repea-containing Rab8b-interacting protein). Our lab recently showed that genetic deletion of HCN channel subunits leads to an antidepressant-like phenotype in mice. Furthermore, others found that decreasing HCN1 in the hippocampus using inhibitory RNA produced similar antidepressant effects, suggesting HCN channel function could be targeted to treat depression. HCN channels are crucial for many functions in the brain and heart, thus pharmaceutical approaches to inhibiting HCN channels could produce unwanted side effects. In contrast, anatomically targeted gene therapy using viral vectors offers the benefit of controlling exactly when and where genes are expressed. In preliminary studies, we found that viral infection of the hippocampus using an adeno-associated virus (AAV) engineered to prevent normal trafficking of HCN subunits in hippocampal neurons (but not control AAV expressing green fluorescent protein) markedly reduced depression-like behavior in tests that screen for antidepressant activity. We thus hypothesize that viral vector-mediated gene therapy to suppress HCN channels in the dorsal hippocampus is an effective treatment for depression. To test this hypothesis, we will use immunohistochemical, biochemical, electrophysiological and behavioral studies to complete the following specific aims: 1) Determine if viral gene therapy targeting HCN channels can produce specific and lasting antidepressant-like effects in mice, and 2) Determine if viral gene therapy targeting HCN channels can effectively eliminate depression-like behaviors in genetic and environmental mouse models of depression. Overall, our proposed work will evaluate a novel target and innovative treatment strategy for depression distinct from all current therapy, with an ultimate goal of translating this therapy to future studies in human patients with depression refractory to existing treatments.