Abstract
The effective treatment of bipolar disorder (BD) represents a significant unmet medical need. Although lithium remains a mainstay of treatment for BD, limited knowledge regarding how it modulates affective behavior has proven an obstacle to discovering more effective mood stabilizers with fewer adverse side effects. One potential mechanism of action of lithium is through inhibition of the serine/threonine protein kinase GSK3β, however, relevant substrates whose change in phosphorylation may mediate downstream changes in neuroplasticity remain poorly understood. Here, we used human induced pluripotent stem cell (hiPSC)-derived neuronal cells and stable isotope labeling by amino acids in cell culture (SILAC) along with quantitative mass spectrometry to identify global changes in the phosphoproteome upon inhibition of GSK3α/β with the highly selective, ATP-competitive inhibitor CHIR-99021. Comparison of phosphorylation changes to those induced by therapeutically relevant doses of lithium treatment led to the identification of collapsin response mediator protein 2 (CRMP2) as being highly sensitive to both treatments as well as an extended panel of structurally distinct GSK3α/β inhibitors. On this basis, a high-content image-based assay in hiPSC-derived neurons was developed to screen diverse compounds, including FDA-approved drugs, for their ability to mimic lithium’s suppression of CRMP2 phosphorylation without directly inhibiting GSK3β kinase activity. Systemic administration of a subset of these CRMP2-phosphorylation suppressors were found to mimic lithium’s attenuation of amphetamine-induced hyperlocomotion in mice. Taken together, these studies not only provide insights into the neural substrates regulated by lithium, but also provide novel human neuronal assays for supporting the development of mechanism-based therapeutics for BD and related neuropsychiatric disorders.
Highlights
Treatment of mental illness represents one of the greatest unmet medical needs of our time[1,2]
To address which phosphorylation sites in the human neural proteome are under the control of GSK3, we first set up to identify candidate targets that are directly changed by pharmacological inhibition of GSK3 in hiPSCderived neural progenitor cells (NPCs) using quantitative SILAC-based mass spectrometry (MS)
Comparative analysis of the two key regulatory GSK3 phosphorylation sites, tyrosine 216 (Tyr216) and serine 9 (Ser9)[50,51,52] (Supplemental Fig. 1a), in human induced pluripotent stem cell (hiPSC)-derived NPCs and neurons suggested different response patterns to CHIR-99021 and lithium treatments (Supplemental Fig. 1), we found that both agents, with different potencies, had a very similar impact on downstream GSK3-dependent WNT signaling gene expression (Supplemental Fig. 2)
Summary
Treatment of mental illness represents one of the greatest unmet medical needs of our time[1,2]. Zhao et al Translational Psychiatry (2020)10:76 of this agent to limit the activity of glycogen synthase kinase-3ß (GSK3β) at therapeutically relevant doses has attracted significant attention[4,5,6,7,8] This interest is supported by the multiple connections that have been established between dysfunction of GSK3 and the pathophysiology of different neuropsychiatric disorders. In combination with accumulating evidence from molecular, cellular, pharmacological, and behavioral studies, have consistently recognized the importance of a balance in the activity of GSK3 for mental health[9,10] In light of these observations, pharmacological control of GSK3 signaling networks is being actively pursued as a potential therapeutic target to treat these severe illnesses
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