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

心境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，目前尚不清楚锂对GSK-3的抑制是否与其抗躁狂和抗抑郁效果有关。我们正在利用生化、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效应机制的一个组成部分。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。具体来说，GSK-3的主要靶点之一是转录因子-连环蛋白。我们已经证明，在临床相关的范例中，给大鼠锂会导致β -连环蛋白水平的增加。我们正在研究β -catenin在小鼠脑中的过表达和低表达的影响以及增加β -catenin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。综上所述，这些数据支持锂可能通过抑制GSK-3发挥其抗抑郁和抗躁狂作用的假设，并且新的小分子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。

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.