Interplay between serotonin 5-HT1A and 5-HT7 receptors in depressive disorders: from molecular mechanisms to behavioral regulation.

5-羟色胺(5-羟色胺或5-羟色胺)是一种重要的神经递质，通过激活异源表达的5-羟色胺受体来调节中枢神经系统内广泛的生理功能。5-羟色胺能系统，特别是5-羟色胺1A受体(5-HT1AR)与严重抑郁障碍(MDD)密切相关，尽管潜在的机制仍是个谜。功能研究也表明5-HT7Rs与抑郁症有关。由于5-HT1a和5-HT7受体在大多数脑结构中共表达，并调节相同的第二信使系统，一个有趣的问题是，在生理和病理条件下，这些受体之间可能存在功能上的串扰。我们先前已经证明，5-HT1AR与5-HT7R形成同源二聚体和异源二聚体。在功能上，异源二聚化抑制5-HT1AR与Gi蛋白的偶联，减弱5-HT1AR介导的钾通道的激活，促进5-HT1AR的内化，而不影响5-HT7R信号转导。此外，我们开发了基于FRET的方法，用于在单细胞水平上同时分析受体寡聚和受体介导的信号转导。我们还证实了5-HT1A和5-HT7受体在5-羟色胺能中缝神经元中的共表达，提示异源二聚化在5-HT1A自身受体的功能调节中起重要作用。最后，我们构建了一组腺病毒载体来调控5-HT1AR和5-HT7R在体内的表达。我们推测，突触前和突触后神经元上调节和平衡的同源和异源二聚化比率可能在MDD的发病和治疗反应中起关键作用。因此，本方案的主要科学问题是5-HT1AR/5-HT7R异二聚化如何调节受体介导的信号，包括在生理和病理条件下不同类型神经元中受体的脱敏和下游效应器的激活。第二个目标是阐明异二聚化在抑郁症样症状的发生、维持和发病机制中的功能作用。为了实现这些目标，我们将应用创新技术的协同组合(例如，小鼠大脑中异二聚体的分析、定量显微镜、FRET、电生理记录、在啮齿动物中应用不同的抑郁模型，以及行为分析)。为了验证异二聚化在人类MDD中的作用，我们将调查以前诊断为主要抑郁症的自杀受害者和对照对象的尸检样本。这些研究的综合结果将极大地提高我们对GPCR寡聚在生理和病理条件下对神经元功能调节的影响的基础知识，为5-HT1AR/5-HT7R异二聚化治疗抑郁症提供可能的治疗作用的信息。

Serotonin (5-hydroxytryptamine or 5-HT) is an important neurotransmitter regulating a wide range of physiological functions within the central nervous system via activation of heterogeneously expressed 5-HT receptors. Serotonergic system and in particular serotonin 1A receptor (5-HT1AR) are critically implicated in major depressive disorder (MDD), although underlying mechanisms remain enigmatic. Functional studies have also implicated 5-HT7Rs in depression. Since 5-HT1A and 5-HT7 receptors are co-expressed in majority of the brain structures and modulate the same second messenger systems, one intriguing question is the possible functional cross-talk between these receptors under physiological and pathological conditions.We have previously shown that the 5-HT1AR forms homo-dimers as well as hetero-dimers with the 5-HT7R. Functionally, hetero-dimerization inhibits coupling of 5-HT1AR to Gi proteins, attenuates 5-HT1AR-mediated activation of potassium channels and facilitates internalization of 5-HT1AR, without affecting 5-HT7R signaling. Moreover, we developed FRET-based approaches for simultaneous analysis of receptor oligomerization and receptor-mediated signaling at the single-cell levels. We also demonstrated co-expression of 5-HT1A and 5-HT7 receptors in serotonergic raphe neurons, suggesting an important role of hetero-dimerization in functional regulation of the 5-HT1A autoreceptor. Finally, we constructed a set of adenoviral vectors to manipulate expression of 5-HT1AR and 5-HT7R in vivo. We hypothesize that regulated and balanced ratio of homo- and hetero-dimerization on pre- and postsynaptic neurons may be critically involved in both the onset as well as the response to treatment of MDD. The main scientific question of the present proposal is thus how 5-HT1AR/5-HT7R hetero-dimerization modulates receptor-mediated signaling, including receptor desensitization and activation of the down-stream effectors in different types of neurons under physiological and pathological conditions. The second goal is to elucidate the functional role of hetero-dimerization in the development, maintenance and pathogenesis of depression-like symptoms. To achieve these goals we will apply a synergistic combination of innovative techniques (e.g. analysis of hetero-dimerization in the mouse brain, quantitative microscopy, FRET, electrophysiological recordings, application of different depression models in rodents, and behavioral analysis). To validate the role of hetero-dimerization in human MDD, we will investigate the post-mortem samples from suicide victims diagnosed previously with major depression and control subjects. The combined outcomes of these investigations will greatly advance our fundamental knowledge about the impact of GPCR oligomerization on regulation of neuronal functions under physiological and pathological conditions, providing information about the possible therapeutic role of 5-HT1AR/5-HT7R hetero-dimerization for treating depression.