Characterizing antidepressant-like effects of a novel peptide HCN channel inhibitor

重度抑郁症（MDD）影响着全世界数百万人。大多数可用于治疗MDD的药物 靶向涉及单胺能神经递质的脑通路。因为百分之五十的病人 并没有改善对现有疗法的反应，靶向新机制的新疗法是 needed.超极化激活的环核苷酸门控（HCN）通道介导Ih，一种重要的 控制神经元兴奋性的电流。大脑HCN通道由一种辅助的 TRIP8b（tetratricopeptide repeat-containing Rab8b-interacting protein）。缺乏TRIP 8b的动物 和其他HCN亚基表现出抗抑郁样表型，这表明抑制HCN通道 可以有效治疗抑郁症。因为这些通道在控制心率方面至关重要， 靶向全身的HCN通道不是可行的治疗方法。我们最近 证明海马中TRIP 8b的病毒过表达导致HCN的变化， 通道功能与抗抑郁药使用相关行为的伴随变化。在 特别是，恢复TRIP 8b基因敲除小鼠海马中的TRIP 8b表达会促进抑郁症- 类似的行为，而TRIP 8b与HCN通道孔形成亚基结合受损的版本 增加抗抑郁症样行为。这些结果表明，TRIP 8b-HCN相互作用可能是一个重要的机制。 用于治疗MDD的新的药理学靶点。 尽管我们最近的病毒基因治疗研究加强了抑制脑HCN可能 对于抑郁症的治疗是有用的，这种方法需要手术，而且技术不容易 可以转化为患有MDD的人类患者。另一方面，TRIP 8b-HCN相互作用的抑制剂提供 在探测HCN通道在行为中的作用方面增加了易用性， 潜在的治疗沿着这些路线，我们已经合成了一种小的（11个氨基酸）肽，能够 在体外结合TRIP 8b并阻断TRIP 8b-HCN相互作用。这种肽的细胞渗透版本 合成SNL-CP以允许肽穿透血脑屏障和细胞膜。在 初步研究表明，SNL-CP穿过CA 1神经元的质膜。我们 假设肽介导TRIP 8b与HCN孔形成相互作用的抑制 亚基将促进抗抑郁样行为。在目标1中，我们将评估SNL-CP的能力， 在小鼠中慢性海马内递送后破坏TRIP 8b-HCN相互作用。这些实验将 确定治疗干预所需的给药策略。在目标2中，我们将评估 SNL-CP促进小鼠的抗抑郁样行为。本提案中所述的工作将评估 一种在小鼠中产生抗抑郁样行为的新方法， 在对现有疗法难治的人类患者中治疗MDD的方法。

Major depressive disorder (MDD) affects millions of people worldwide. Most drugs available to treat MDD target brain pathways involving monoaminergic neurotransmitters. Because up to fifty percent of patients do not improve in response to existing therapies, new treatments that target novel mechanisms are needed. Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels mediate Ih, an important current for controlling neuronal excitability. Brain HCN channels are tightly regulated by an auxiliary subunit, TRIP8b (tetratricopeptide repeat-containing Rab8b-interacting protein). Animals lacking TRIP8b and other HCN subunits exhibit an antidepressant-like phenotype, suggesting that inhibiting HCN channels could effectively treat depression. Because the channels are critical in controlling heart rate, directly targeting HCN channels throughout the body is not a viable therapeutic approach. We recently demonstrated that viral overexpression of TRIP8b in the hippocampus leads to changes in HCN channel function with concomitant changes in behaviors associated with antidepressant use. In particular, restoring TRIP8b expression in the hippocampi of TRIP8b knockout mice promoted depression- like behaviors, while a version of TRIP8b with impaired binding to HCN channel pore-forming subunits increased antidepressant-like behavior. These results indicate that the TRIP8b-HCN interaction might be a novel pharmacological target for treating MDD. Although our recent studies with viral gene therapy strengthen the evidence that inhibiting brain HCN might be useful for depression treatment, the approach requires surgery and the technology is not readily translatable to human patients with MDD. On the other hand, inhibitors of the TRIP8b-HCN interaction offer increased ease of use in probing the role of HCN channels in behavior as well as greater translatability as potential therapies. Along theses lines, we have synthesized a small (11 amino acids) peptide capable of binding TRIP8b and blocking the TRIP8b-HCN interaction in vitro. A cell permeable version of this peptide (SNL-CP) was synthesized to allow the peptide to penetrate the blood-brain barrier and cell membranes. In preliminary studies, we show that SNL-CP crosses the plasma membrane of CA1 neurons. We hypothesize that peptide mediated inhibition of TRIP8b's interaction with HCN pore-forming subunits will promote antidepressant-like behavior. In aim 1, we will assess the ability of SNL-CP to disrupt the TRIP8b-HCN interaction after chronic intrahippocampal delivery in mice. These experiments will determine the dosing strategy necessary for therapeutic intervention. In aim 2, we will evaluate the ability of SNL-CP to promote antidepressant-like behavior in mice. The work described in this proposal will evaluate a novel approach to producing antidepressant-like behaviors in mice and could pave the way for a new approach to treating MDD in human patients refractory to existing therapies.