Testing whether the enzyme GSK-3 is a therapeutically relevant target of lithium

情绪稳定剂锂抑制一组选定的酶，包括糖原合成酶激酶-3（GSK-3）。然而，目前尚不清楚锂抑制GSK-3是否与其抗躁狂和抗抑郁有效性相关。我们正在利用生物化学，细胞，组织化学，基因组和行为验证方法来研究GSK-3的抑制是否是锂临床作用机制的组成部分。我们正在利用啮齿动物行为模型和两种不同但互补的方法（药理学抑制和转基因基因表达），试图进一步验证GSK-3作为锂治疗效果的可能介质。具体而言，GSK-3的主要靶点之一是转录因子β-连环蛋白。我们已经表明，在临床相关的范例中，锂给药大鼠导致β-连环蛋白水平增加。我们正在研究β-连环蛋白在小鼠大脑中过度表达和表达不足的影响，以及增加β-连环蛋白的药理学机制。使用这些方法，我们发现啮齿动物在治疗后表现出抗抑郁样和抗躁狂样行为。综合起来，这些数据支持这样的假设，即锂可以通过抑制GSK-3发挥其抗抑郁和抗躁狂作用，并且新型小分子GSK-3抑制剂可能代表了一种真正的新型药物，可用于治疗双相情感障碍和抑郁症。锂治疗靶点的验证将需要新型抑制剂的临床试验，其开发正在进行中。 像锂一样，GSK-3抑制剂发挥抗躁狂和抗抑郁功效。然而，GSK-3抑制影响情绪行为的分子机制尚不清楚。越来越多的证据表明，神经元能突触传递在双相情感障碍的病理生理学和治疗中起着重要作用，这表明阐明GSK-3调节突触可塑性的机制，特别是神经元能突触传递，可能会阐明GSK-3抑制剂产生情绪稳定作用的共同途径。 我们发现GSK-3抑制剂AR-A014418可调节谷氨酸受体亚型（称为α-氨基-3-羟基-5-甲基-4-异恶唑丙酸酯（AMPA）受体）的细胞内化，包括谷氨酸受体1（GluR1）和谷氨酸受体2（GluR2）。我们发现GluR1和GluR2的内化通过驱动蛋白轻链2（KLC 2）的磷酸化发生，KLC 2是驱动蛋白货物递送系统的关键分子。具体而言，AMPA刺激触发KLC 2的丝氨酸磷酸化，随后，GluR1/KLC 2蛋白复合物的解离。这表明GSK-3磷酸化KLC 2导致含AMPA的囊泡从驱动蛋白货物系统中解离。肽TAT-KLCpCDK是GSK-3 β对KLC 2磷酸化的特异性抑制剂，它减少了称为长期抑郁（LTD）的记忆相关过程的形成和AMPA受体的内化。此外，TAT-KLCpCDK肽对安非他明诱导的小鼠多动症表现出类似于锂的抗躁狂作用，以及在悬尾试验中的抗抑郁作用。总之，结果确定了细胞机制，KLC 2磷酸化，作为GSK-3 β调节突触可塑性的新靶点，特别是与AMPA受体运输和情绪相关行为相关。这种驱动蛋白货物系统提供了有价值的新的目标，为情绪障碍的新疗法的发展。这一发现也是首次阐明锂情绪稳定作用的分子机制。

The mood stabilizer lithium inhibits a select group of enzymes, including glycogen synthase kinase-3 (GSK-3). However, it is unclear if lithium inhibition of GSK-3 is relevant for its antimanic and antidepressant effectiveness. We are utilizing biochemical, cellular, histochemical, genomic, and behavioral validation approaches to investigate whether the inhibition of GSK-3 is an integral part of the mechanism of lithiums clinical effects. We are utilizing rodent behavioral models and two distinct but complementary approaches (pharmacologic inhibition and transgenic gene expression) in an attempt to further validate GSK-3 as a possible mediator of lithiums therapeutic effects. Specifically, one of the primary targets of GSK-3 is the transcription factor beta-catenin. We have shown that lithium administration to rats in a clinically relevant paradigm results in an increase in beta-catenin levels. We are studying the effects of both over-expression and under-expression of beta-catenin in the mouse brain as well as pharmacological mechanisms to increase beta-catenin. Using these approaches, we have found that rodents exhibit both antidepressant-like and antimanic-like behavior after treatment. Combined, these data support the hypothesis that lithium may exert its antidepressant and antimanic effects through inhibition of GSK-3, and that novel small-molecule GSK-3 inhibitors may represent a truly novel class of medications useful for the treatment of bipolar disorder and depression. Validation of lithiums therapeutic target will require clinical trials with novel inhibitors, the development of which is in progress. Like lithium, GSK-3 inhibitors exert both antimanic and antidepressant efficacy. However, the molecular mechanism through which GSK-3 inhibition influences emotional behavior is unknown. Accumulating evidence suggests that glutamatergic synaptic transmission plays a major role in the pathophysiology and treatment of bipolar disorder, suggesting that elucidation of the mechanism via which GSK-3 modulates synaptic plasticity, and particularly glutamatergic synaptic transmission, may illuminate the common pathway whereby GSK-3 inhibitors produce mood stabilizing effects. We found that GSK-3 inhibitors AR-A014418 regulated the cellular internalization of a glutamate receptor subtype known as the alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA) receptor, including Glutamate receptor 1 (GluR1) and Glutamate Receptor 2 (GluR2). We found that GluR1 and GluR2 internalization occurs via phosphorylation of kinesin light chain 2 (KLC2), the key molecule of the kinesin cargo delivery system. Specifically, AMPA stimulation triggered serine phosphorylation of KLC2 and, subsequently, the dissociation of the GluR1/KLC2 protein complex. This suggests that GSK-3 phosphorylation of KLC2 led to the dissociation of AMPA-containing vesicles from the kinesin cargo system. The peptide TAT-KLCpCDK, a specific inhibitor for KLC2 phosphorylation by GSK-3beta, reduced both the formation of a memory-related process called long-term depression (LTD) and the internalization of AMPA receptors. Furthermore, the TAT-KLCpCDK peptide showed an anti-manic effect similar to lithium on amphetamine-induced hyperactivity in mice, as well as an antidepressant effect in the tail suspension test. Taken together, the results identified a cellular mechanism, KLC2 phosphorylation, as a novel target of GSK-3beta to regulate synaptic plasticity, particularly associated with AMPA receptor trafficking and mood-associated behaviors. This kinesin cargo system provides valuable novel targets for the development of new therapeutics for mood disorders. The findings are also the first to elucidate the molecular mechanism of action for lithium's mood stabilizing effects.