CHIR99021 causes inactivation of Tyrosine Hydroxylase and depletion of dopamine in rat brain striatum

Abstract

CHIR99021, also known as laduviglusib or CT99021, is a Glycogen-synthase kinase 3{beta} (GSK3{beta}) inhibitor, which has been reported as a promising drug for cardiomyocyte regeneration or treatment of sensorial hearing loss. Since the activation of dopamine (DA) receptors regulates dopamine synthesis and they can signal through the {beta}-arrestin pathway and GSK3{beta}, we decided to check the effect of GSK3{beta} inhibitors (CHIR99021, SB216763 and lithium ion) in the control of DA synthesis. Using ex vivo experiments with minces from rat brain striatum, we observed that CHIR99021, but not SB216763 nor lithium, causes a complete abrogation of DA synthesis and accumulation at low {micro}M concentrations, pointing to off-target effects of CHIR99021. This decrease can be attributed to tyrosine hydroxylase (TH) inhibition since the accumulation of L-DOPA in the presence of a DOPA decarboxylase inhibitor was similarly decreased. On the other hand, CHIR99021 caused a dramatic increase in the DOPAC / DA ratio, an indicator of DA metabolization, and hindered DA incorporation into striatum tissue to the same extent as tetrabenazine, thus pointing to some effect on DA storage that triggers DA feedback inhibition of TH. In addition, CHIR99021 or SB216763, but not lithium, decreased TH phosphorylation in Ser19, but not in Ser31 or Ser40. These results demonstrate that CHIR99021 can lead to TH inactivation and DA depletion in brain striatum, opening the possibility of its use in DA-related disorders, and shows effects to be considered in future clinical trials.